1. Field of the Invention
This invention relates to the separation of particles from a liquid in which the particles are suspended, more particularly, the separation of blood cells from the blood plasma or the blood serum in which they are suspended.
2. Discussion of the Art
For in vitro diagnostics, biological samples currently used are samples of blood plasma or samples of blood serum. Samples of blood plasma and samples of blood serum are used because of potential physical interferences with detection (e.g., light scattering or absorption caused by blood cells) and chemical interferences caused by lysis of red blood cells (which alters the composition of the specimen). Disease markers related to proteins, lipoproteins, hormones, antibodies, antigens, viruses, bacteria, and parasites are commonly detected in blood plasma or blood serum of a patient. In order to collect blood plasma or blood serum, red blood cells, white blood cells, platelets, and other components must be removed from a sample of whole blood. Blood plasma makes up about 55% of total blood volume. It is composed mostly of water (90% by volume) and contains dissolved proteins, glucose, clotting factors, mineral ions, hormones, and carbon dioxide (plasma being the main medium for excretory product transportation). Blood serum is blood plasma without fibrinogen or the other clotting factors. Blood cells must be removed from blood plasma or blood serum before the sample of blood can be analyzed.
Centrifugation and filtration are currently used to separate blood cells from blood plasma or blood serum for diagnostic purposes. Both techniques require extensive labor and a relatively great amount of time for medical laboratories, which have limited resources with respect to both equipment and personnel. The drawbacks of centrifugation, wherein samples of whole blood are introduced into a centrifuge rotating at from about 1500 to about 3400 rpm, typically from about 3000 to about 3400 rpm, for 10 to 15 minutes, include consumption of time, which results from the time needed by a technician to load and unload samples and the need for a skilled technician to aspirate blood plasma or blood serum with a pipette from the separated layers in blood collection tubes. Up to 25% of the time consumed in medical laboratories involves centrifugation of samples. The drawbacks of filtration processes include fouling of the filter and low throughput after fouling occurs. A finite filter capacity and problems with non-specific binding on account of the large surface area of a filter are problematic with respect to filtration steps. Other potential problems include breakage of blood collection tubes and loss of the sample. There is also the risk of hemolysis and the consequent destruction of the sample. Accordingly, it would be desirable to provide a method that is cost effective and efficient for the separation of blood cells from blood plasma or blood serum in order to analyze a sample of blood.
Burd et al., U.S. Pat. No. 5,186,844, discloses an analytical rotor for separating cellular components from a biological fluid. The rotor includes a separation chamber spaced radially outward from the sample chamber. The sample chamber may be an open receptacle disposed to receive sample or may be a mixing chamber which receives sample and diluent. A flow restrictive channel connects the sample chamber to the separation chamber so that fluid enters the separation chamber at a controlled rate. The cellular components collect within a retention region located generally at the outer periphery of the collection chamber while cell-free fluid is continuously removed through a collection port. The collection is spaced annularly apart from the flow channel so that there is sufficient residence time within the separation chamber for substantially complete separation of the cells from the fluid fraction.
Effenhauser, et al., U.S. Patent Application Publication No. US 2005/0029190, discloses a method for separating particles from a fluid dispersion, particularly for separating corpuscular components from biological samples, above all, from blood. A separating module suitable for performing the method has a substrate with flow channels, comprising a feed channel for supplying the dispersion to a junction, a first drain channel for draining fluid having a reduced particle concentration away from the junction, and a second drain channel for draining fluid having an increased particle concentration away from the junction. The fluid flows so much faster in the second drain channel than in the first drain channel that due to different flow speeds the dispersed particles preferentially flow at the junction further in the second drain channel.
Blattert et al., U.S. Patent Application Publication No. US 2006/0204400, discloses a process for separation of dispersions or suspensions by applying an external pressure gradient between a feed reservoir and at least one waster reservoir in such a way that the dispersion flows into a microchannel system. At least one fraction is separated through an opening and via at least one target channel. Different flows in a waster channel and a target channel of the microchannel system are set by the selection of an external pressure gradient. The various phases in a dispersion or suspension are separated and concentrated further by a series arrangement of structures of bend arcs. An apparatus for carrying out the process connects the feed reservoir and at least one waste reservoir via a feed channel, at least one bend arc and further channels, respectively, the fractions of the dispersion or the suspension separated substantially within the at least one bend arc.
Fan et al., “Integrated Blood Barcode Chips”, Nat Biotechnol. 2008 December; 26(12): 1373-1378, published online 2008 Nov. 16. doi: 10.1038/nbt.1507, discloses an integrated microfluidic system that enables on-chip blood separation and the rapid measurement of a panel of plasma proteins from small quantities of blood samples including a fingerprick of whole blood. The article discloses a polydimethylsiloxane (PDMS)-on-glass chip designed for 8-12 separate multi-protein assays to be executed sequentially, or in parallel, starting from whole blood. The plasma separation was achieved by exploiting the Zweifach-Fung effect of highly polarized blood cell flow at branch points of small blood vessels. This hydrodynamic effect was utilized by flowing blood through a low-flow-resistance primary channel that has high-resistance, centimeter long channels branching off perpendicularly. As the resistance ratio is increased between the branches and the primary channel, a critical streamline moves closer to the primary channel wall adjoining the branch channels. Blood cells with a radius larger than the distance between this critical streamline and the primary channel wall are directed away from the high-resistance channels, and about 15% of the plasma is skimmed into the high-resistance channels. The remaining whole blood is directed towards a waste outlet. The glass base of the plasma-skimming channels is pre-patterned, prior to the microfluidics chip assembly, with a dense barcode-like array of ssDNA oligomers. A full barcode is repeated multiple times within a single plasma-skimming channel, and each barcode sequence constitutes a complete assay.